The present application relates to a semiconductor structure and a method of forming the same. More particularly, the present application relates to a SOI lateral heterojunction Si-emitter SiGe-base bipolar transistor that includes a step germanium distribution in the base region which results in a step energy band gap in the base that provides a high unity gain bandwidth, fT, and a high maximum oscillation frequency, fmax. The present application also provides a method of forming such a SOI lateral heterojunction Si-emitter SiGe-base bipolar transistor.
Bipolar junction transistors are typically found in demanding types of analog circuits, especially analog circuits used in high-frequency applications. For example, bipolar junction transistors can be found in radio frequency integrated circuits (RFICs) used in wireless communication systems, as well as integrated circuits requiring high power efficiency, such as power amplifiers in cellular telephones, and other types of high speed integrated circuits. Bipolar junction transistors may be combined with complementary metal-oxide-semiconductor (CMOS) field effect transistors in bipolar complementary metal-oxide-semiconductor (BiCMOS) integrated circuits, which take advantage of the favorable characteristics of both transistor types.
Conventional bipolar junction transistors, such as vertical bipolar transistors, include three semiconductor regions, namely the emitter, base, and collector regions. Generally, a bipolar junction transistor includes a pair of p-n junctions, namely an emitter-base junction and a collector-base junction. A heterojunction bipolar transistor (HBT) is a variety of a bipolar junction transistor that employs at least two semiconductor materials with unequal band gaps for the emitter/collector and base regions, creating a heterojunction.
With the advent of semiconductor-on-insulator (SOI) technology, innovative thin-base lateral bipolar transistors such as, for example, a SOI lateral heterojunction Si-emitter SiGe-base bipolar transistor, have been developed. A need exists for providing SOI lateral heterojunction Si-emitter SiGe-base bipolar transistors that have a higher unity gain bandwidth, fT, and a higher maximum oscillation frequency, fmax, than presently available SOI lateral heterojunction Si-emitter SiGe-base bipolar transistors.